Surgical microscopes using optical coherence tomography and related systems

ABSTRACT

Some embodiments of the present inventive concept provide optical coherence tomography (OCT) systems for integration with a microscope. The OCT system includes a sample arm coupled to the imaging path of a microscope. The sample arm includes an input beam zoom assembly including at least two movable lenses configured to provide shape control for an OCT signal beam; a scan assembly including at least one scanning mirror and configured for telecentric scanning of the OCT signal beam; and a beam expander configured to set the OCT signal beam diameter incident on the microscope objective. The shape control includes separable controls for numerical aperture and focal position of the imaged OCT beam.

CLAIM OF PRIORITY

The present application claims priority to and is a divisional of U.S.application Ser. No. 13/836,576, filed Mar. 15, 2013, which claimspriority from U.S. Provisional Application No. 61/620,645, filed Apr. 5,2012, the disclosures of which are hereby incorporated herein byreference as if set forth in their entirety.

STATEMENT OF GOVERNMENT SUPPORT

This inventive concept was funded in-part with government support underGrant Application ID R44EY018021-03 by the National Institutes ofHealth, National Eye Institute. The United States Government has certainrights in this inventive concept.

FIELD

The present inventive concept relates to surgical microscopes and, moreparticularly, to ophthalmic surgical microscopes using optical coherencetomography (OCT).

BACKGROUND

Surgical microscopes provide a magnified view of the operating field tothe surgeon. Ophthalmic surgical microscopes are commonly stereo zoommicroscopes with binocular view ports for the surgeon, and frequentlyhave one or two observer view ports at ninety degrees (left and right)to the surgeon. The working distance between the objective lens of themicroscope and the surface of a patient eye may range from about 100 mmto about 200 mm. At this working distance, which provides a suitablefield of access for the manual work of the surgeon, the field of viewwithin a patient eye may be quite limited. It is quite common to use anintermediate lens, such as the Binocular Indirect Ophthalmo Microscope(BIOM) of Oculus Optikgerat, to modify the magnification and field ofview for the surgeon. This intermediate lens is mounted to theunder-carriage of the microscope head, and includes mechanics to adjustfocus, and to flip the lens into and out of the field of view of themicroscope.

Other illumination or imaging devices may also be used in the surgicalfield. Ideally, all illumination and imaging sources would be directlyintegrated coaxial to and within the optical path of the operatingmicroscope, without impacting the operating field for the surgeon, theobservers, the anesthesiologists, and the like. It is still desirable toprovide a readily maneuverable mount for imaging and other accessoriesthat is closely coupled to the surgical field, utilizing the mechanicalcontrols and attributes that are already integral to a well-functioningoperating microscope, without degrading the visual attributes of theoperating microscope.

A particular case of interest is the incorporation of optical coherencetomography (OCT) imaging into the surgical visualization practice. OCTprovides high resolution imaging of ocular tissue microstructure, and isshowing great promise to provide information to the surgeon that willimprove therapeutic outcomes, and reduce the total economic burdens ofsurgery by reducing risk and reducing re-work.

Conventional frequency domain. OCT (FDOCT) systems will now be discussedto provide some background related to these systems. Referring first toFIG. 1A, a block diagram of an FDOCT retinal imaging system will bediscussed. As illustrated in FIG. 1A, the system includes a broadbandsource 100, a reference arm 110 and a sample arm 140 coupled to eachother by a beamsplitter 120. The beamsplitter 120 may be, for example, afiber optic coupler or a bulk or micro-optic coupler. The beamsplitter120 may provide from about a 50/50 to about a 90/10 split ratio. Asfurther illustrated in FIG. 1A, the beamsplitter 120 is also coupled toa wavelength or frequency sampled detection module 130 over a detectionpath 106 that may be provided by an optical fiber.

As further illustrated in FIG. 1A, the source 100 is coupled to thebeamsplitter 120 by a source path 105. The source 100 may be, forexample, a continuous wave broadband superluminescent diode, a pulsedbroadband source, or tunable source. The reference arm 110 is coupled tothe beamsplitter 120 over a reference arm path 107. Similarly, thesample arm 140 is coupled to the beamsplitter 120 over the sample armpath 108. The source path 105, the reference arm path 107 and the samplearm path 108 may all be provided by optical fiber or a combination ofoptical fiber, free-space, and bulk- or micro optical elements.

As illustrated in FIG. 1A, the reference arm of the FDOCT retinalimaging system may include a collimator assembly 180, a variableattenuator 181 that may include a neutral density filter or a variableaperture, a mirror assembly 182, a reference arm variable path lengthadjustment 183 and a path length matching position 150, i.e. opticalpath length matching between the reference arm path length and thesample arm path length to the subject region of interest. As furtherillustrated, the sample arm 140 may include a dual-axis scanner assembly190 and an objective lens with variable focus 191.

The sample illustrated in FIG. 1A is an eye including a cornea 195,iris/pupil 194, ocular lens 193 and retina 196. A representation of anFDOCT imaging window 170 is illustrated near the retina 196. The retinalimaging system relies on the objective lens plus the optics of thesubject eye, notably cornea 195 and ocular lens 193, to image theposterior structures of the eye. As further illustrated the region ofinterest 170 within the subject is selected through coordination of thefocal position 196 and reference arm path length adjustment 183, suchthat the path length matching position 197 within the subject is at thedesired location.

Referring now to FIG. 1B, a block diagram illustrating a FDOCT corneal(anterior) imaging system will be discussed. As illustrated therein, thesystem of FIG. 1B is very similar to the system of FIG. 1A. However, theobjective lens variable focus need not be included, and is not includedin FIG. 1B. The anterior imaging system of FIG. 1B images the anteriorstructures directly, without reliance on the optics of the subject tofocus on the anterior structures.

As discussed above, ophthalmic surgical microscopes can provide surgeonsa magnified view of various areas of the eye on which they areoperating. However, there are many ophthalmic surgical procedures thatmay benefit from the kind of high-resolution depth-resolved imagingprovided by Optical Coherence Tomography (OCT). Thus, integrating an OCTsystem into a surgical microscope may provide greater capabilities andenable procedures that currently cannot be performed with conventionalstereoscopic imaging.

As illustrated in FIG. 1C, there are various regions of interest in theeye, which may require different OCT imaging characteristics. Forexample, referring to FIG. 1C, region 1, the corneal region, typicallyrequires relatively high resolution OCT imaging. A fairly largedepth-of-focus (DOF) is desirable to allow the entire corneal structureto be imaged. Such imaging is desirable in support of cornea transplantprocedures. Likewise, imaging of the crystalline lens, region 2,benefits from high resolution imaging of the capsular structure. A largeDOF is required to visualize the entire lens at one time. By contrast,structures on the retina, region 3, lie in a constrained depth region,and tend to be very fine. Thus, retinal imaging typically requires veryhigh resolution, but not necessarily a large DOF.

Existing surgical microscopes incorporating OCT will be discussed withrespect to FIGS. 1D and 1E. Referring first to FIG. 1D, like referencenumerals refer back to FIGS. 1A and 1B. However, as illustrated in FIG.1D, a stereo zoom microscope 160 has been incorporated into the samplearm path 108. As illustrated, the surgical microscope 160 includes twooculars (binocular view ports) 162 for the surgeon to view the sample199. The surgical microscope 160 of FIG. 1D includes a beamsplitter 161,where the beamsplitter may be a dichroic filter, and an objective lens163 positioned beneath the dichroic filter 161. As further illustratedthe sample arm path 108 is coupled to a collimator 165 that forms a beamexiting an optical fiber and a pair of galvos 190 which directs the beamto the dichroic filter 161 integrated into the infinity space of themicroscope between the ocular paths 162 and the main objective 163. Thebeam reflects off the dichroic filter 161 and through the objective lens163 to image the sample 199, which may be an eye or any other accessibleregion of a subject. The microscope 160 illustrated in FIG. 1D is astatic surgical microscope, i.e. dynamic adjustments to the focallengths are not possible; focal changes are possible only by exchange ofoptical elements (installing a new main objective lens 163) or changingthe working distance between the microscope 160 and the subject 199.

Referring now to FIG. 1E another design of a surgical microscopeincorporating OCT will be discussed. Surgical microscopes illustrated inFIG. 1E are discussed in U.S. Pat. No. 8,366,271 to Izatt et al., thedisclosure of which is incorporated herein by referenced as if set forthin its entirety. As illustrated in FIG. 1E, the surgical microscopesystem of FIG. 1E is similar to the system of FIG. 1D except a telescopelens assembly set 167 is provided between the pair of galvos 190 and thedichroic filter 161 of the surgical microscope 163. Thus, in the systemof FIG. 1E, the beam travels through the galvos 190 into the telescopelens set 167 and then through the dichroic filter 161 through theobjective lens 163 to image the sample 199. The presence of thetelescope lens set 167 provides beam shaping to maximize the numericalaperture of the system, potentially improving the lateral resolution ofthe images produced by the system, however, the system illustrated inFIG. 1E offers limited flexibility in modifying or controlling thecharacteristic of the scanning beam.

SUMMARY

Some embodiments of the present inventive concept provide opticalcoherence tomography (OCT) systems for integration with a microscope.The OCT system includes a sample arm coupled to the imaging path of amicroscope. The sample arm includes an input beam zoom assemblyincluding at least two movable lenses configured to provide shapecontrol for an OCT signal beam; a scan assembly including at least onescanning mirror and configured for telecentric scanning of the OCTsignal beam; and a beam expander configured to set the OCT signal beamdiameter incident on the microscope objective. The shape controlincludes separable controls for numerical aperture and focal position ofthe imaged OCT beam.

In further embodiments, the OCT signal beam may be coupled to themicroscope imaging path through a beamsplitter. The beamsplitter may beset at an angle of not less than 48 degrees and not greater than 55degrees relative to the optical axis of the microscope objective. Thebeamsplitter may be a dichroic filter.

In still further embodiments, the beam expander may include anaberration compensator.

In some embodiments, a path length adjustment may be included in thesample arm between the beam expander and the microscope objective toaccommodate for variances in the focal length of the microscopeobjective.

In further embodiments, the telecentric scan assembly may include afirst scanning having a first image that is relayed onto a secondscanning mirror. An exit pupil of the OCT sample arm may be in the backfocal plane of the microscope objective. The exit pupil of the OCTsample arm optics may be a virtual exit pupil.

In still further embodiments, the input beam zoom may include first andsecond positive lenses and a negative lens therebetween. The numericalaperture of the system may be set by controlling a first distancebetween the first positive lens and the negative lens and a seconddistance between the negative lens and the second positive lens. A focusof the OCT system may be set by controlling a position of the secondpositive lens for a particular setting of numerical aperture.

In some embodiments of the present inventive concept, at least a portionof the OCT path may occupy a center channel of the microscope. The OCTbeam may be directed towards a center field of the microscope objective.Any ocular paths of the microscope may be situated peripherally to thiscenter field of the microscope objective.

In further embodiments, the beamsplitter may occupy an area less than aclear aperture of the microscope objective.

In still further embodiments, the sample may be an eye. A retinalimaging lens assembly may be situated between the microscope objectiveand the eye. The retinal imaging lens assembly may image a conjugate ofthe scanning mirrors to a position posterior to the pupil plane of eye.The retinal imaging lens assembly may include at least one lens with atleast one aspheric surface.

In some embodiments, an objective lens may be provided in common with amicroscope. The objective lens may be anti-reflection coated foroperation in a visible spectral range relevant to the microscopevisualization and an infrared spectral range relevant to the OCT system.The microscope objective may be an achromatic doublet comprising a crownglass positive lens component and flint glass negative lens component.

Further embodiments of the present inventive concept provide methods ofoptical coherence tomography (OCT) imaging in conjunction with asurgical procedure. The methods include visualizing a first region ofinterest having an image depth of z₁ using a spectral sampling intervalof v₁; and visualizing a second region of interest having an image depthof z_(z) using a spectral sampling interval v₂, wherein v₂ is greaterthan or equal to 2v₁.

In still further embodiments, visualizing the first region of interestmay be performed with a scanning system having a first numericalaperture. Visualizing the second region of interest may be performedwith the scanning system having a second numerical aperture, differentfrom the first numerical aperture, the second numerical aperture beinggreater than the first numerical aperture.

Some embodiments of the present inventive concept provided methods ofoptical coherence tomography (OCT) imaging in conjunction with asurgical procedure. The method includes establishing a first setting ofa region of interest for OCT imaging; establishing a first numericalaperture and a first focal position for the OCT imaging; acquiring atleast a first OCT image; calculating at least a first clinical parameterfrom the at least first OCT image; performing a surgical procedure;acquiring at least a second OCT image; and computing at least a secondclinical parameter from the at least a second OCT image.

Further embodiments of the present inventive concept provide methods ofoptical coherence tomography (OCT) imaging in conjunction with asurgical procedure. The method includes setting a first region ofinterest within a surgical sample for OCT imaging; acquiring at least afirst OCT image of the first region of interest; performing a surgicalprocedure involving the first region of interest; setting a secondregion of interest within the surgical sample for OCT imaging, thesecond region of interest being at least partially different from thefirst region of interest; and acquiring at least a second OCT image ofthe second region of interest.

In still further embodiments, a first reference arm position, a firstnumerical aperture, and a first focal position may be set for acquiringthe OCT image in the first region of interest. At least one of areference arm position, a numerical aperture and a focal position maybechanged for acquiring the OCT image in the second region of interest.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram illustrating an example OCT retinal(posterior) imaging system.

FIG. 1B is a block diagram illustrating an example Optical CoherenceTomography (OCT) cornea (anterior) imaging system.

FIG. 1C is a diagram illustrating various regions of interest in theeye.

FIG. 1D is a block diagram illustrating an example surgical microscope.

FIG. 1E is a block diagram illustrating an example surgical microscopeincluding a telescoping lens set.

FIG. 2A is a block diagram of a surgical microscope in accordance withsome embodiments of the present inventive concept.

FIG. 2B is a block diagram of a surgical microscope in accordance withsome embodiments of the present inventive concept.

FIG. 3 is a more detailed block diagram of a modified retinal lensillustrated in FIG. 2B used in accordance with some embodiments of thepresent inventive concept.

FIG. 4A is a block diagram of an OCT center channel surgical microscopein accordance with some embodiments of the present inventive concept.

FIG. 4B is a block diagram of an OCT center channel surgical microscopein accordance with some embodiments of the present inventive concept.

FIG. 4C is a detailed block diagram of the OCT portion of the OCT centerchannel surgical microscope illustrated in FIGS. 4A-4B.

FIGS. 5A through 5C are a side view, front view and oblique view,respectively, of an OCT system interface in accordance with someembodiments of the present inventive concept.

FIGS. 6A through 6C various views of an OCT system integrated with asurgical microscope in accordance with some embodiments of the presentinventive concept.

FIG. 7A is a block diagram illustrating a block diagram of anOCT-Integrated Surgical Microscope in accordance with some embodimentsof the present inventive concept

FIG. 7B is a block diagram illustrating a block diagram of an OCT systemincluding an Integrated Surgical Microscope in accordance with someembodiments of the present inventive concept.

FIG. 7C is a block diagram illustrating an OCT system suitable forintegrating with Surgical Microscope in accordance with some embodimentsof the present inventive concept.

FIG. 8 is a diagram illustrating an OCT optical path for surgicalimaging in accordance with embodiments of the present inventive concept.

FIG. 9A is a schematic diagram illustrating a layout of an OCT systemintegrated into the path of a Surgical Microscope in accordance withsome embodiment of the present inventive concept.

FIG. 9B is a diagram illustrating a collimator and Input Beam Zoom (IBZ)system in accordance with some embodiments of the present inventiveconcept.

FIG. 9C is a diagram illustrating changing numerical aperture (NA) andswitching regions of focus with the IBZ in accordance with someembodiments of the present inventive concept.

FIG. 10 is a block diagram illustrating a telecentric relay system inaccordance with some embodiments of the present inventive concept.

FIG. 11 is a diagram illustrating a relay beam expander (RBE) system inaccordance with some embodiments of the present inventive concept.

FIG. 12 is a diagram illustrating a high performance objective lens foran OCT surgical microscope in accordance with some embodiments of thepresent inventive concept.

FIG. 13 is a series of graphs and charts illustrating telecentricoptical performance in accordance with some embodiments of the presentinventive concept.

FIG. 14 is a series of graphs and charts illustrating telecentricoptical performance in accordance with some embodiments of the presentinventive concept.

FIG. 15 is a series of graphs illustrating the optical performance whenshifting focus with a 150 mm objective lens in accordance with someembodiments of the present inventive concept.

FIG. 16 is a series of graphs illustrating the optical performance whenshifting focus with a 160 mm objective lens in accordance with someembodiments of the present inventive concept.

FIG. 17 is a series of graphs illustrating the optical performance whenshifting focus with a 175 mm objective lens in accordance with someembodiments of the present inventive concept.

FIGS. 18A and 18B are block diagrams illustrating conventionalconfigurations for surgical retinal imaging and a configuration inaccordance with embodiments of the present inventive concept,respectively.

FIG. 19A is a diagram of a surgical retina lens assembly forOCT-integrated surgical microscopy having a wide FOV in accordance withsome embodiments of the present inventive concept.

FIG. 19B are a series of graphs and diagrams illustrating opticalperformance of the surgical retina lens of FIG. 19A in accordance withsome embodiments of the present inventive concept.

FIG. 20A is diagram illustrating a lens system for a surgical lensassembly for OCT-integrated surgical microscopy having a wide FOV inaccordance with some embodiments of the present inventive concept.

FIG. 20B is a diagram illustrating a summary of optical performance ofthe surgical lens assembly of FIG. 20B in accordance with someembodiments of the present inventive concept.

FIG. 21A is diagram illustrating a lens system for a surgical lensassembly for OCT-integrated surgical microscopy having a narrow FOV inaccordance with some embodiments of the present inventive concept.

FIG. 21B is a diagram illustrating a summary of optical performance ofthe surgical lens assembly of FIG. 21A in accordance with someembodiments of the present inventive concept.

FIG. 22A is diagram illustrating a lens system for a surgical lensassembly having a narrow FOV in accordance with some embodiments of thepresent inventive concept.

FIG. 22B is a diagram illustrating a summary of optical performance ofthe surgical lens assembly of FIG. 22A in accordance with someembodiments of the present inventive concept.

FIG. 23A is diagram illustrating a lens system for a surgical lensassembly having a mid-range FOV in accordance with some embodiments ofthe present inventive concept.

FIG. 23B is a diagram illustrating a summary of optical performance ofthe surgical lens assembly of FIG. 23A in accordance with someembodiments of the present inventive concept.

FIG. 24 is a diagram illustrating OCT telecentricity conditions inaccordance with some embodiments of the present inventive concept.

FIG. 25 is a diagram illustrating Afocal Relay Zoom Lens conditions of aSurgical Stereo Microscope in accordance with some embodiments of thepresent inventive concept.

FIG. 26 is a diagram illustrating conditions of an OCT center channelOCT-integrated Surgical Stereo Microscope in accordance with someembodiments of the present inventive concept.

FIG. 27 is a diagram illustrating conditions of folded path OCT centerchannel OCT-integrated Surgical Stereo Microscope in accordance withsome embodiments of the present inventive concept.

FIG. 28 is a flowchart illustrating a method of imaging using anOCT-integrated surgical microscope in accordance with some embodimentsof the present inventive concept.

FIG. 29 is a flowchart illustrating a method of imaging during asurgical procedure using an OCT-integrated surgical microscope inaccordance with some embodiments of the present inventive concept.

FIG. 30 is a series of charts illustrating image depth of fieldadjustment through selection of spectral sampling interval in accordancewith some embodiments of the present inventive concept.

FIG. 31 is a diagram illustrating an optical layout for anOCT-integrated microscope in accordance with some embodiments of thepresent inventive concept.

DETAILED DESCRIPTION

The present inventive concept will be described more fully hereinafterwith reference to the accompanying figures, in which embodiments of theinventive concept are shown. This inventive concept may, however, beembodied in many alternate forms and should not be construed as limitedto the embodiments set forth herein.

Accordingly, while the inventive concept is susceptible to variousmodifications and alternative forms, specific embodiments thereof areshown by way of example in the drawings and will herein be described indetail. It should be understood, however, that there is no intent tolimit the inventive concept to the particular forms disclosed, but onthe contrary, the inventive concept is to cover all modifications,equivalents, and alternatives falling within the spirit and scope of theinventive concept as defined by the claims. Like numbers refer to likeelements throughout the description of the figures.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the inventiveconcept. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises”, “comprising,” “includes” and/or “including” when used inthis specification, specify the presence of stated features, integers,steps, operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, components, and/or groups thereof. Moreover, whenan element is referred to as being “responsive” or “connected” toanother element, it can be directly responsive or connected to the otherelement, or intervening elements may be present. In contrast, when anelement is referred to as being “directly responsive” or “directlyconnected” to another element, there are no intervening elementspresent. As used herein the term “and/or” includes any and allcombinations of one or more of the associated listed items and may beabbreviated as “/”.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this inventive concept belongs. Itwill be further understood that terms used herein should be interpretedas having a meaning that is consistent with their meaning in the contextof this specification and the relevant art and will not be interpretedin an idealized or overly formal sense unless expressly so definedherein.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement without departing from the teachings of the disclosure. Althoughsome of the diagrams include arrows on communication paths to show aprimary direction of communication, it is to be understood thatcommunication may occur in the opposite direction to the depictedarrows.

Although many of the examples discussed herein refer to the sample beingan eye, specifically, the retina, cornea, anterior segment and lens ofthe eye, embodiments of the present inventive concept are not limited tothis type of sample. Any type of sample that may be used in conjunctionwith embodiments discussed herein may be used without departing from thescope of the present inventive concept.

As discussed above, ophthalmic surgical microscopes can provide surgeonsa magnified view of various areas of the eye on which they areoperating. However, there are many ophthalmic surgical procedures thatmay benefit from the kind of high-resolution depth imaging provided byOptical Coherence Tomography (OCT). Thus, integrating an OCT system intoa surgical microscope may provide greater capabilities and enableprocedures that currently cannot be performed with only conventionalstereoscopic imaging. Conventional surgical microscopes incorporatingOCT generally provide static imaging incapable of adapting for theregion of interest in the sample. Taking the example of an eye,conventional systems cannot typically adapt to the difference imagingrequirements for imaging the corneal region, the anterior chamber andcrystalline lens, and the structures on the retina.

An ideal OCT surgical microscope system would be adaptable to tailor theimaging characteristics for the various regions of interest. An idealOCT surgical microscope would have the following set of attributes: truetelecentric scanning for accurate representation of subject topography;variable numerical aperture to control the distribution of illuminationover a depth of field and to allow control of lateral resolution at theposition of focus; variable focus to allow independent control of theOCT focal position relative to the ocular focus of the visualmicroscope; a wide field of view wherein the scanning optical pathlength is held maximally constant, both to keep physiopathology withinthe OCT depth of field and to avoid visual distortions of the scannedfield; and adjustability to accommodate a wide range of microscope mainobjectives, to provide versatility to the surgeon for various surgicalprocedures. It is further desirable to minimize any alterations to thephysical working distances of the microscope to which the surgeon may beaccustomed. These distances include the distance between the mainobjective and the subject, and the distance between the microscopeoculars and the subject.

Existing systems do not address all of the desired set of attributes.The standard configuration for OCT scanning places two orthogonalscanning mirrors in close proximity. In such a condition, telecentricitymay be optimized along one axis only. Some systems project a firstmirror onto a second; this is a necessary but not sufficient conditionto achieve telecentricity. One object of this invention is to enable atelecentric scanning system over a wide field of view. In an embodimentof the present invention, the system images to a field flatness of lessthan 5 micrometers over an area of 400 square millimeters (20 mm fieldof view).

The telescopic beam expansion proposed in Izatt and other related art iseffective at changing a focal position and a numerical aperture, butthese parameters are coupled. In such a configuration it is not possibleto independently control a focal position and a numerical aperture. Oneobject of this invention is to provide for independent control of afocal position of the scanning OCT beam and the numerical aperture ofthe beam. In an embodiment of the present invention, the numericalaperture may be controlled such that the beam waist is variable betweenapproximately 9 micrometers and 25 micrometers. Further, in hisembodiment the focal position may be adjusted by more than 1.5 mm in thehigh numerical aperture condition (narrow beam waist) and more than 15mm in the low numerical aperture condition (wide beam waist), and thefocus and numerical aperture may be controlled independently.

In OCT imaging through a BIOM or related surgical retina lens, theoptical path length of the scanning OCT beam varies widely across thefield of view, such that the retina appears strongly curved, and suchthat beyond approximately a 50 degree field of view the optical pathlength difference between the center and the edges of the retinal may begreater than 4 mm. In such a case the periphery of the retina may notvisible in the OCT image. It is an object of this invention to present amodified surgical retina lens to equalize the optical path length of anOCT image across a wider field of view. In an embodiment of the presentinvention, the optical path length difference in an OCT scan across a100 degree field of view of the retina is less than approximately 2 mm.

In prior presentations of OCT surgical microscopes, the designs envisionone fixed main objective for the surgical microscope. No accommodationhas been foreseen for adjusting the OCT system to a range of mainobjectives as may suit the surgeon for different procedures. It is anobject of this invention for the sample arm of the OCT system toaccommodate a range of main objectives. In an embodiment of thisinvention, the OCT system adapts to main objectives with a range offocal lengths between 150 mm and 200 mm, with additional embodimentsaccommodating broader or narrower ranges, or ranges centered aroundshorter or longer working distances.

In prior presentations of OCT surgical microscopes, a dichroic mirror isinjected at 45 degrees to couple the OCT beam into the surgical imagingpath. In such a configuration, the path length between the oculars andthe subject increases in known proportion to the clear aperture of themain objective. It is an object of this invention to minimize thisincrease in working lengths without impacting the usable aperture of themain objective. In one embodiment of the invention, the dichroic mirroris set an angle other than 45 degrees, reducing the impact on workingdistances. In a further embodiment of the present invention a modifiedmain objective is introduced that additionally reduces the impact onworking distances. In yet another embodiment of the invention, an OCTcenter channel configuration is introduced that has still less impact onworking distances.

Finally, since an ophthalmic surgical microscope is typically mounted atthe end of an articulating arm to provide adjustability and access forthe surgeon, an OCT surgical microscope system is typically very compactand lightweight so as not to affect the performance of the microscope.

Accordingly, embodiments of the present inventive concept provide OCTsurgical microscopes capable of adapting to the various regions of thesample as will be discussed further herein with respect to FIGS. 2Athrough 31.

Referring first to FIG. 2A, a block diagram of an OCT surgicalmicroscope in accordance with some embodiments of the present inventiveconcept will be discussed. As illustrated in FIG. 2A, the systemincludes a broadband source 200, a reference arm 210 and a sample arm240 coupled to each other by a beamsplitter 220. The beamsplitter 220may be, for example, a fiber optic coupler or a bulk or micro-opticcoupler. The beamsplitter 220 may provide from about a 50/50 to about a90/10 split ratio. As further illustrated in FIG. 2A, the beamsplitter220 is also coupled to a wavelength or frequency sampled detectionmodule 230 over a detection path 206 that may be provided by an opticalfiber.

As further illustrated in FIG. 2A, the source 200 is coupled to thebeamsplitter 220 by a source path 205. The source 200 may be, forexample, a superluminescent light emitting diode (SLED) or tunablesource. The reference arm 210 is coupled to the beamsplitter 220 over areference arm path 207. Similarly, the sample arm 240 is coupled to thebeamsplitter 220 over the sample arm path 208. The source path 205, thereference arm path 207 and the sample arm path 208 may all be providedby optical fiber.

As further illustrated in FIG. 2A, the surgical microscope 255 includestwo oculars (binocular view ports) 262 for the surgeon to view thesample 299. The surgical microscope 255 of FIG. 2A includes a modifieddichroic filter 256 and an optimized objective lens 259 in accordancewith embodiments discussed herein. The objective lens 259 is positionedbeneath the dichroic filter 259 as illustrated in FIG. 2A. Aconventional objective lens of a stereo surgical microscope isconfigured to perform in the visible spectrum. OCT uses the infraredspectrum. Thus, the objective lens 259 in accordance with embodimentsdiscussed herein is modified to extend the wavelength range of theobjective lens to allow imaging using OCT and improve the imagesprovided by the surgical microscope using OCT. Furthermore, theobjective lens 259 in accordance with embodiments discussed herein maybe configured to be thinner than a conventional lens, thus, reducing theworking distance. Details of the objective lens 259 in accordance withembodiments of the present inventive concept will be discussed furtherbelow.

Referring again to FIG. 2A, as further illustrated the sample arm path208 is coupled to an input beam zoom (IBZ) 250, a telecentric scanassembly 251, a beam expander 252 and an optional back focal lengthadjuster 254 which provide the beam to the modified dichroic filter 256integrated into the surgical microscope. The beam travels through thedichroic filter 256 and into the objective lens 259 to image the sample299, which may be an eye in some embodiments.

The input beam zoom (IBZ) 250 is provided for input beam shape control.Details of IBZs in accordance with various embodiments discussed hereinwill be discussed further below. However, IBZs are discussed in detailin commonly assigned U.S. patent application Ser. No. 13/705,867, filedon Dec. 5, 2012, the entire contents of which is hereby incorporatedherein by reference as if set forth in its entirety.

The telecentric scan assembly 262 controls the telecentricity of thesystem. For example, the telecentric scan assembly 262 in accordancewith some embodiments may include a telecentric galvo relay lens (GRLs)pair, i.e. a first GRL half (GRLH) and a second GRLH. Each GRLH may bedesigned as a modified Wild eyepiece. However, telecentric scanassemblies 262 are discussed in detail in commonly assigned U.S. patentapplication Ser. No. 13/705,867, filed on Dec. 5, 2012, the entirecontents of which was incorporated herein in its entirety above.

The beam expander 254 (relay beam expander (RBE)) is an afocal RBEsystem, the details of which will be discussed further below. Theobjective back focal length adjuster 254 provides adjustment to a rangeof main objectives. Thus, embodiments of the present inventive conceptprovide an OCT system having an objective lens that can adapt to changesin focal length. In other words, typically when the focal length isadjusted at the front, it also needs to be compensated at the back, i.e.back focal length adjustment.

Although the RBE 252 and the objective back focal length adjuster 254are illustrated in FIG. 2A as separate modules, embodiments of thepresent inventive concept are not limited to this configuration. Forexample these two modules 252 and 254 may be combined without departingfrom the scope of the present inventive concept. Similarly, although thevarious modules of FIG. 2A are illustrated as separate blocks, theseblocks can be combined or separated into more blocks without departingfrom the scope of the present inventive concept. The OCT systemillustrated in FIG. 2A is a system that is optimized for telecentricimaging of the anterior segment of the eye of a subject or otherstructures directly accessible and visible to the surgical microscope.

Surgical microscopes in accordance with some embodiments of the presentinventive concept include an “infinity space.” This is a space above thefinal objective lens before the stereo beams converge. For example, inFIG. 2A, the dichroic filter 256 is inserted into this “infinity space.”This space with one or more spectrally diverse or polarization diversefilters may be used to couple additional accessories to the surgicalmicroscope system. Accessories may include, but are not limited to, forexample, a video camera, wavefront analysis system, an auto refractor, ascanning laser ophthalmoscope and/or a laser. In some cases the couplingelement will be within the infinity space, but in some cases a couplingelement may exist elsewhere in the OCT signal path. These embodimentswill be discussed further below.

Referring now to FIG. 2B, a block diagram of an OCT surgical microscopein accordance with some embodiments of the present inventive conceptwill be discussed. Like reference numbers in FIG. 2B refer to likeelements in FIG. 2A, thus, details of these elements will not berepeated in the interest of brevity. As discussed above, it is quitecommon to use an intermediate lens, such as the Binocular IndirectOphthalmo Microscope (BIOM) of Oculus Optikgerat, to modify themagnification and field of view for the surgeon. This intermediate lensis mounted to the under-carriage of the microscope head, and includesmechanics to adjust focus, and to flip the lens into and out of thefield of view of the microscope. The BIOM is a retinal imaging lens thatallows the microscope to switch between viewing anterior and posteriorstructures of the eye. However, the BIOM retinal lens is not optimizedfor use with OCT and thus an improved retinal lens is needed for usewith an OCT surgical microscope.

As illustrated in FIG. 2B, a retinal lens 258 (surgical retina lensassembly) in accordance with some embodiments of the present inventiveconcept is positioned beneath the objective lens 259. The retinal lens258 is modified in accordance with embodiments discussed herein foroptimized use with OCT and is configured to adjust accordingly. Asillustrated in FIG. 3, the retina lens (surgical retina lens assembly)includes a condenser 340 and a modified retina lens 342. The retina lens342 allows the focus to be moved down to the retina. Details withrespect to the modified surgical retinal lens assembly having variousfields of view (FOV) will be discussed further below.

It will be understood that the surgical microscope should be as compactas possible to allow enough room for the surgeon to perform theprocedure between the objective lens of the microscope and thesample/patient. In other words, there needs to be a reasonable workingdistance between the patient and the microscope so the surgeons handscan comfortable perform the procedure. Accordingly, some embodiments ofthe present inventive concept provide the dichroic filter and the OCTportion of the OCT surgical microscope in a center channel of thesurgical microscope itself as will be discussed with respect to FIGS. 4Athrough 4C below.

Referring first to FIG. 4A, a block diagram of a center channel surgicalmicroscope in accordance with some embodiments of the present inventiveconcept will be discussed. As illustrated in FIG. 4A, the systemincludes a broadband source 400, a reference arm 410 and a sample armintegrated in a center channel of the OCT surgical microscope 453. Thebroadband source 400, the reference arm 410 and the OCT surgicalmicroscope 453 are coupled to each other by a beamsplitter 420. Thebeamsplitter 420 may be, for example, a fiber optic coupler or a bulk ormicro-optic coupler. The beamsplitter 420 may provide from about a 50/50to about a 90/10 split ratio, generally such that light backscatteredfrom the samples couples preferentially to the detection path. Asfurther illustrated in FIG. 4A, the beamsplitter 420 is also coupled toa wavelength or frequency sampled detection module 430 over a detectionpath 406 that may be provided by an optical fiber.

As further illustrated in FIG. 4A, the source 400 is coupled to thebeamsplitter 420 by a source path 405. The source 400 may be, forexample, a SLED or tunable source. The reference arm 410 is coupled tothe beamsplitter 420 over a reference arm path 407. Similarly, thesurgical microscope 453 is coupled to the beamsplitter 420 over thesample arm path 408. The source path 405, the reference arm path 407 andthe sample arm path 408 may all be provided by optical fiber.

As further illustrated in FIG. 4A, the surgical microscope 453 includestwo oculars (binocular view ports) 462 for the surgeon to view thesample 499. The surgical microscope 453 of FIG. 4A may, but need not,include a dichroic filter (not shown) and an optimized objective lens459 in accordance with embodiments discussed herein. The dichroic, whenused, allows the OCT to be folded into the path in a way to partiallyshare the clear aperture occupied by the ocular paths. In someembodiments of the present invention, the OCT center channel occupiesthe center field of the main objective. The dichroic may also be used tocouple additional accessory element.

In some embodiments of the present invention where the dichroic is notused, the OCT center channel occupies the center field of the mainobjective, and the ocular channels occupy a peripheral portion of themain objective aperture.

In embodiments of the present inventive concept illustrated in FIG. 4A,the OCT optics or a subset thereof 4445 are integrated into a centerchannel of the surgical microscope 453. The OCT sample arm 445 ispositioned in the center channel of the surgical microscope 453. Theobjective lens 259 is positioned beneath the OCT portion 445.

Referring now to FIG. 4B, a block diagram of a center channel surgicalmicroscope in accordance with some embodiments of the present inventiveconcept will be discussed. Like reference numbers in FIG. 4B refer tolike elements in FIG. 4A, thus, details of these elements will not berepeated in the interest of brevity. As illustrated in FIG. 4B, aretinal lens 458 (surgical retina lens assembly) in accordance with someembodiments of the present inventive concept is positioned beneath theobjective lens 459. The retinal lens 458 in accordance with embodimentsdiscussed herein is optimized for use with OCT and is configured toadjust accordingly. As illustrated in FIG. 3 discussed above, the retinalens (surgical retina lens assembly) includes a condenser 340 and aretina lens 342 that may be modified to reduce the optical path lengthdifference for the OCT scan beam across the field of view of the retina.Details with respect to the surgical retinal lens assembly havingvarious FOVs will be discussed further below.

Referring now to FIG. 4C, a detailed block diagram of the OCT portion ofthe center channel surgical microscope illustrated in FIGS. 4A-4B willbe discussed. As illustrated in FIG. 4C, the OCT portion 445 includesthe IBZ 450′, the telecentric scan assembly 451′, the beam expander 452′and an optional back focal length adjuster 454′ as discussed above withrespect to FIG. 2A. The beam travels through the objective lens 459, andany subsequent accessory lenses 458 to image the sample 499, which maybe an eye in some embodiments.

Referring now to FIGS. 5A through 5C, a side view, front view andoblique view, respectively, of an OCT system interface in accordancewith some embodiments of the present inventive concept are illustratedtherein. In this representative embodiment, the OCT system is coupledinto the “infinity space” of the microscope with the addition of adichroic filter above the microscope main objective. In an embodiment ofthe present invention, the dichroic filter is situated at an anglegreater than 45 degrees with respect to the microscope viewing path. Inthis situation, the angle of the OCT input with respect to the pathbetween the objective lens and the sample is less than 90 degrees, asillustrated in FIG. 5B. The vertical space occupied by the dichroicfilter sets the minimum addition to the working distances for thesurgeon. The minimum vertical space requirement is equal to the clearaperture of the main objective divided by the tangent of the angle ofthe dichroic. At 45 degrees, the minimum vertical space requirement isequal to the objective clear aperture, and the OCT beam enters thecoupling space at 90 degrees. With the angle increased to 50 degrees,vertical space requirement is reduced to 84% of the objective clearaperture, and the OCT beam enters the coupling space an angle of 80degrees with respect to the vertical axis, or 10 degrees with respect tothe horizontal.

In the 45 degree dichroic configuration, with the OCT entering theimaging path at 90 degrees, the OCT beam diameter may be configured tofully illuminate the clear aperture of the main objective, as suggestedby Izatt. This condition is not always desirable for optimum imagingperformance, as will be illustrated in discussions below. It isimportant however to maintain an unvignetted OCT beam path. As thedichroic is tilted away from 45 degrees and the OCT beam enters the beampath from an angle at less than 90 degrees, the maximum aperture of theOCT beam is constrained. Through a geometric analysis, the maximumaperture of the OCT beam as a fraction of the main objective aperturecan be described by Eqn. (1) below:F=[1−2*T/(1+T)]

Where F equals the ratio of the maximum unvignetted OCT beam diameter tothe clear aperture of the main objective, and T is a geometric functiondescribed in Eqn. (2) below:T=Tan(2*θ−π/2)*Tan(θ)

Where θ is equal to the angle of the dichroic filter with respect to theoptical axis of the main objective (such that 90 degrees isperpendicular to the optical axis).

In an embodiment of the present invention, the filter angle θ is greaterthan 45 degrees and less than 60 degrees. In another embodiment of theinvention, the filter angle is greater than 48 degrees, such that thereis at least a 10% reduction in the vertical space requirement for theOCT entry beam, and less than 55 degrees, such that the maximumunvignetted OCT beam diameter is at least 30% of the main objectiveclear aperture. In yet another embodiment of the invention, the filterangle is greater than 50 degrees, such that there is at least a 15%reduction in the vertical space requirement for the OCT entry beam, andless than 54 degrees, such that the maximum unvignetted OCT beamdiameter is at least 40% of the main objective clear aperture. In stillanother embodiment of the invention, the filter angle is set atapproximately 53 degrees, such that there is at approximately a 25%reduction in the vertical space requirement for the OCT entry beam, andsuch that the maximum unvignetted OCT beam diameter is approximately 45%of the main objective clear aperture.

Referring now to FIGS. 6A through 6C various views of an OCT systemintegrated with a surgical microscope in accordance with someembodiments of the present inventive concept are illustrated therein. Insome embodiments, the surgical microscope may be a Leica M844 surgicalmicroscope. However, embodiments of the present inventive concept arenot limited to this configuration. Embodiments of the present inventiveconcept may be used with any surgical microscope without departing fromthe scope of the present inventive concept. FIG. 6A is a plan view ofthe OCT system integrated with a surgical microscope in accordance withsome embodiments discussed herein. FIGS. 6B and 6C are side and topviews, respectively.

Referring now to FIG. 7A, a block diagram of an OCT-Integrated SurgicalMicroscope in accordance with some embodiments of the present inventiveconcept will be discussed. As illustrated in FIG. 7A, the OCT integratedsurgical microscope system includes a surgical microscope 255, 453, abeam forming unit, an objective compensating unit, beam combiners, amain objective, a retina lens 258, 458 or other accessory lens, asubject 299, 499 and accessory channels 735 as discussed above withrespect to FIG. 2A.

As further illustrated in FIG. 7A, the beam forming unit includes theIBZ 250, 450, the telecentric scanner 251, 451 and the beam expander252, 452. The objective compensating unit includes the back focal lengthadjust (BFLA) 254, 454. The beam combiners include one or more dichroicfilters 256, 456 having different spectral bands (e.g. D1, D2). The mainobjective includes an objective lens 259, 459 that may be modified inaccordance with embodiments discussed herein. As further illustrated,accessory channels may be provided in the “infinity space” Or elsewherein the OCT imaging path. These Accessories may include, but are notlimited to, for example, a video camera, a wavefront analysis system, anauto refractor, a scanning laser ophthalmoscope (SLO) and/or a laser,for example, a CW/Pulse Laser.

Referring now to FIG. 7B, a block diagram illustrating an OCT-IntegratedSurgical Microscope in accordance with some embodiments of the presentinventive concept will be discussed. As illustrated in FIG. 7A, the OCTintegrated surgical microscope system includes a beam forming unit, anobjective compensating unit, beam combiners, a main objective,supplemental objectives 734, a sample under test 299, 499 and accessorychannels 735. In this diagram, the OCT system is viewed as a primaryimaging system, and the surgical microscope is one of a possibleplurality of combined modalities.

As further illustrated in FIG. 7B, the beam forming unit includes theIBZ 250, 450, the telecentric scanner 251, 451 and the beam expander252, 452. The objective compensating unit includes the back focal lengthadjust (BFLA) 254, 454. The beam combiners include dichroic filters 259,459 having different spectral bands (D1, D2 . . . DN). The mainobjective includes an objective lens 259, 459 that may be modified inaccordance with embodiments discussed herein. Accessories may include,but are not limited to, for example, a surgical scope, a video camera, awavefront analysis system, an auto refractor, a scanning laserophthalmoscope (SLO), a laser, for example, a CW/Pulse Laser, a femtosecond laser and/or other accessory.

Referring now to FIG. 7C, a block diagram illustrating a generalizedconstruction of an OCT-Integrated Surgical Microscope in accordance withsome embodiments of the present inventive concept will be discussed. Asillustrated in FIG. 7C, the OCT integrated surgical microscope systemincludes a beam forming unit, an objective compensating unit, beamcombiners, a main objective, supplemental objectives 734 and a subject299, 499.

As further illustrated in FIG. 7C, the beam forming unit includes theIBZ 250, 450, the telecentric scanner 251, 451 and the beam expander252, 452. The objective compensating unit includes the back focal lengthadjust (BFLA) 254, 454. The beam combiners include dichroic filters 259,459 having different spectral bands (D1, D2). The main objectiveincludes a modified objective lens 259, 459 in accordance withembodiments discussed herein. Optional accessories may be coupledthrough the beam combiners which may be wavelength dependent (dichroic)or polarization dependent.

Referring now to FIG. 8, a diagram illustrating an OCT optical path forsurgical imaging in accordance with some embodiments of the presentinventive concept will be discussed. As illustrated therein, the portionif the optical path labeled (1) represents the IBZ; the portion of theoptical path labeled (2) represents the telecentric relay; the portionof the optical path labeled (3) represents the RBE; and the portion ofthe optical path labeled (4) represents the objective lens in accordancewith embodiments of the present inventive concept.

FIG. 9A is a schematic diagram illustrating another layout of an IO-OCTsystem in accordance with some embodiment of the present inventiveconcept. FIG. 9A illustrates a system layout including components usedand a representation of first-order (thin lens) parameters. The inputcollimator assembly (COL) includes the Input Beam Zoom, and is followedby the telecentric relay from galvo mirror 1 (GM1) to galvo mirror 2(GM2), and then expended by the afocal relay from relay lens 1 (RL1)through relay lens 2 (RL2). First-order equations relating all thesystem optical parameters were derived for two extreme limiting cases ofnumerical aperture that bracketed the performance space: a high NA (HNA)case with high lateral resolution and low DOF; and a low NA (LNA) casewith low lateral resolution and high DOF. These equations were used tocalculate an estimated overall system length from input fiber source toeye. The design space was mapped out for various driving parameters,such as input beam diameter and working distance, and a solution thatprovides a reduced overall system length was chosen for this embodiment.

With this chosen first-order system design, various methods of NA andfocal plane control were evaluated. It was determined that an IBZ systembetween the collimated input beam and the first scanning galvo mirrorcould provide the required control over NA and, thus, lateral resolutionand DOF, and focal plane location. A second-order (thick lens) designwas generated for the IBZ system. In some embodiments, this zoom systemconsists of 3 singlets as illustrated, for example, in FIG. 9B, onenegative lens element (c) and two identical positive elements (b) and(d).

In operation, the first positive element (b) stays fixed, while thenegative (c) and last positive (d) element positions are modified to seta continuous range of focal and numerical aperture conditions. A forwardmotion of the negative element (c), accompanied with a shorterretrograde motion of the last positive element (d) allows the IBZ systemto go from a HNA to LNA configuration, and can be coordinated to do soat constant focal position. Motion of the last positive element (d)adjusts the system focal plane location: backward motion moves the focalplane forward with respect to the subject (i.e. deeper into the eye). Inthese embodiments, all the variation can be accomplished with two lenselement motions. Furthermore, this zoom system may be located prior tothe scanning optical system allowing for modular system design anddecreased system complexity.

Referring again to FIG. 8, with the IBZ specified, a second-order (thicklens) design was generated for the remainder of the system illustratedin FIG. 8. The primary sub-systems following the IBZ are, in transmittedlight incidence order: the first scanning galvo mirror (X); the galvorelay lens (GRL) system; the second, orthogonal scanning galvo mirror(Y); and the afocal relay beam expander (RBE) system. The GRL definesthe optical system pupil, locates it at the first (X) galvo mirror, andimages it to the second (Y) galvo mirror. The RBE system then imagesthis system pupil with the required magnification to the back focalplane of the surgical microscope objective lens. This last condition, incombination with the relay of the X galvo to the Y galvo, is a necessarycondition allowing the system to be telecentric in the focal plane ofthe microscope objective. This condition may lead to a long optical pathlength for the OCT scanning system. A further optional feature of theinventive design is to design the optics such that the system pupil isvirtual, allowing the location of the system pupil to overlap precedinglens elements, thereby reducing the overall system length and theoptical path length of the system while maintaining systemtelecentricity.

As discussed above, FIG. 9B is a diagram illustrating a collimator (a)and Input Beam Zoom (IBZ) (b, c, and d) system in accordance with someembodiments of the present inventive concept.

Referring now to FIG. 9C, a diagram illustrating changing numericalaperture (NA) and switching regions of interest with the IBZ inaccordance with some embodiments of the present inventive concept willbe discussed. As illustrated the collimator lens (a) is followed by theIBZ including (b) a first positive lens, (c) a first negative lens and(d) a second positive lens.

As used herein, the “input beam zoom” refers to the zoom factor as afunction of first and second lens spacing, D1 and D2 illustrated in FIG.9C. The zoom factor controls the numerical aperture (NA). For example,at zoom factor=1, the system is in low NA mode. As zoom factorincreases, the NA of the system increases. As discussed above, the firstlens spacing (D1) is the distance to the negative lens (c) from thefirst positive lens (b) and the second lens spacing (D2) is the distanceto the final positive lens (d) from the negative lens (c).

At any zoom setting, focus may be adjusted by movement of the final lens(c) of the IBZ. Increasing the second lens spacing (D2) increases thefocal power of the IBZ, and shortens the focal length of the system.Reducing the second lens spacing (D2) reduces the focal power of the IBZand increases the focal length of the system. It will be noted that twodegrees of freedom, lens spacing D1 and lens spacing D2, provide acontinuous range of control of system numerical aperture and focus. Therange of control is dependent on the available physical space formovement of the lenses, the respective powers of the lenses, and thedownstream imaging optics, as will be understood by one skilled in theart. It will also be noted that the imaging conditions aredeterministic, and multiple modes of control may be employed to achievea desired state, including without limitation, sequential orsimultaneous movement of lens, movement according to values set in alookup table, or adjustment with feedback based on positional encodersor in response to image quality feedback.

Thus, in case (1) illustrated in FIG. 9C, the spacings D1, D2 result inhigh numerical aperture (NA) (e.g. the maximum NA for the specificconfiguration). In case (2), the negative lens (c) moves +9.8 mm and thepositive lens (d) moves −2.6 mm to result in low NA. In case (3), fromthe low NA position of case (2), the positive lens(d) moves −5.6 mm toresult in low NA and deepened focus.

Referring now to FIG. 10, a block diagram illustrating a telecentricrelay system in accordance with some embodiments of the presentinventive concept will be discussed. As illustrated therein, thetelecentric relay system, for example, elements 251 and 451 discussedabove, may include (a) a Doublet nearest Galvo #1 (X); (b) a Singlet;(c) a Singlet; (d) a Doublet; (e) a Conjugate Plane; (f) a Doublet; (g)a Singlet; (h) a Singlet; and (i) a Doublet nearest Galvo #2 (Y). As isclear from the block diagrams discussed above, the telecentric relaysystem 251, 451 follows the IBZ 250, 450.

Referring now to FIG. 11, a diagram illustrating a relay beam expander(RBE) system in accordance with some embodiments of the presentinventive concept will be discussed. As illustrated the RBE system, forexample, elements 252, 452 discussed above, may include (j) a Beamexpander input Doublet nearest Galvo #2(Y); (k) a Singlet; (l) aSinglet; (m) a Doublet; (n) a Doublet; (o) an aberration correctingCompensating Singlet; (p) a Singlet; and (q) and a Beam expander outputDoublet, nearest the microscope main objective. The compensating singlet(o) is designed to correct for essential aberrations that are known toarise from imaging with a basic achromatic doublet that comprises themicroscope objective. As is clear from the block diagram discussedabove, the telecentric relay system (251, 451) discussed with respect toFIG. 10 is coupled to the RBE system 252, 452 discussed with respect toFIG. 11 and both proceed the objective lens as discussed above.

Referring now to FIG. 12, a diagram illustrating a high performanceobjective lens for an OCT surgical microscope in accordance with someembodiments of the present inventive concept. As illustrated in FIG. 12,the objective lens may include crown glass and flint glass. The crownglass may have an edge thickness of about 3.4 mm. The objective lensillustrated in FIG. 12 is a 70 mm high transmission lens having an axialthickness of about 27 mm (160 mm), 25 mm (175 mm). This objective isthinner than a standard commercial microscope objective, has betterimaging optical properties through a low fractional partial dispersion,improving the bandwidth of the objective to incorporate the visiblespectrum for the microscope and the near infrared imaging for the OCT.

In some embodiments, the Crown Glass S-FPL51 (n_(d)=1.497, v_(d)=81.5)(Extra low dispersion glass) and the Flint Glass S-NBH5 (n_(d)=1.654,v_(d)=39.7). In these embodiments, a low ΔP/Δv is wanted to improve asecondary spectrum, where P=partialdispersion=(n_(F)−n_(d))/(n_(F)−n_(C)) and v=Abbe vnumber=(n_(d)−1)/(n_(F)−n_(C)). In some embodiments, F=486 nm, d=588 nmand C=656 nm.

In an embodiment of the present invention, the microscope objective isanti-reflection coated for operation in the visible and infraredspectrums relevant to the microscope and the OCT system, respectively.

FIG. 13 is a series of graphs and charts illustrating telecentricoptical performance of a 150 mm objective lens at nominal focus inaccordance with some embodiments of the present inventive concept. A 150mm objective lens represents a relatively short focal length objectivethat might be used in an ocular surgical procedure. In FIG. 13, the OCTspot size at the telecentric focal plane is shown across the 10 mmhalf-field of view, in the limits of high numerical aperture (HNA) asset by the IBZ, and low numerical aperture (LNA). The spot diametersrange from 10 um (HNA) to 25 um (LNA), constant across the field ofview. Telecentricity is quantified as both field flatness, or opticalpath length difference (OPLD) for the scanned OCT beam, and maximumangle of incidence deviation from perpendicular for rays incidence onthe focal plane. The maximum OPLD is 1.7 μm, or 0.017% of the field ofview, and the deviation from perpendicularity is 0.067 degrees.

FIG. 14 is a series of graphs and charts illustrating telecentricoptical performance of a 175 mm objective lens at nominal focus inaccordance with some embodiments of the present inventive concept. A 175mm objective lens represents a typical objective that might be used inan ocular surgical procedure. In FIG. 14, the OCT spot size at thetelecentric focal plane is shown across the 10 mm half-field of view, inthe limits of high numerical aperture (HNA) as set by the IBZ, and lownumerical aperture (LNA). The spot diameters range from 11 um (HNA) to27 um (LNA), constant across the field of view. The maximum OPLD is 1.7μM, or 0.017% of the field of view, and the deviation fromperpendicularity is 0.061 degrees.

FIG. 14 is a series of graphs and charts illustrating telecentricoptical performance of a 175 mm objective lens at nominal focus inaccordance with some embodiments of the present inventive concept. A 175mm objective lens represents a typical objective that might be used inan ocular surgical procedure. In FIG. 14, the OCT spot size at thetelecentric focal plane is shown across the 10 mm half-field of view, inthe limits of high numerical aperture (HNA) as set by the IBZ, and lownumerical aperture (LNA). The spot diameters range from 11 um (HNA) to27 um (LNA), constant across the field of view. The maximum OPLD is 1.7um, or 0.017% of the field of view, and the deviation fromperpendicularity is 0.061 degrees.

FIG. 15 is a series of graphs and charts illustrating opticalperformance of a 150 mm objective lens while shifting the OCT focus inaccordance with some embodiments of the present inventive concept,demonstrating an ability to shift focus 1.7 mm deeper at constant spotsize for the HNA case, and 20 mm deeper at LNA. Similar performance isachieved in focusing shallower, though not shown in the figure.

FIG. 16 is a series of graphs and charts illustrating exemplary opticalperformance of a 160 mm objective lens while shifting the OCT focus inaccordance with some embodiments of the present inventive concept,demonstrating an ability to shift focus at least 2 mm deeper at constantspot size for the HNA case, and at least 10 mm deeper at LNA. Similarperformance is achieved in focusing shallower, though not shown in thefigure.

FIG. 17 is a series of graphs and charts illustrating exemplary opticalperformance of a 1675 mm objective lens while shifting the OCT focus inaccordance with some embodiments of the present inventive concept,demonstrating an ability to shift focus at least 2.4 mm deeper atconstant spot size for the HNA case, and at least 12 mm deeper at LNA.Similar performance is achieved in focusing shallower, though not shownin the figure.

FIGS. 18A and 18B are block diagrams illustrating conventionalconfigurations for an accessory surgical retina imaging lens assemblyand a configuration in accordance with embodiments of the presentinventive concept, respectively. As illustrated in FIG. 18A, using aconventional objective lens, a conventional reduction lens and aconventional retina lens (e.g. BIOM), the pivot point of the OCT scan inthe eye is imaged into the pupil plane of an eye. This is a typicalposition for OCT imaging, and is particularly well suited tononvignetted OCT imaging of a non-mydriatic (non-dilated) eye. However,the pupil plane in a human eye is not at the center of curvature of theretina of the eye. The optical path length from pupil center to theperiphery of the retina is generally significantly short than theoptical path length to the center, or macular region of the retina.Having a pivot point in the pupil plane will cause the scan to scanaround the pupil, which will cause the OCT image to look highly curvedas shown in FIG. 18A. As illustrated therein, the OPLD (Optical pathlength distortion)=OPLc (optical path length to the center of theretina)−OPLe (optical path length to the edge of the retina), which willtypically be in the range of about 3 mm-4 mm in an adult eye.

In stark contrast, using an optimized objective lens 259, 459 andmodified retinal lens system 258, 458 in accordance with embodiments ofthe present inventive concept, the pivot of the scanning OCT beam isshifted towards the center of curvature of the retina as shown in FIG.18B. Moving the pivot point further back in the eye provides a muchflatter OCT image. Thus, as illustrated in FIG. 18B, the OPLD ofembodiments of the present inventive concept would be less than 2 mm,which is a dramatic improvement for a typical OCT system designed toimage a retina with a 2 mm to 3 mm imaging depth window. This designobjective requires a mydriatic (dilated) eye or severe vignetting mayoccur. Dilation is commonly used in surgery, and therefore this presentsno disadvantage. This is in stark contrast to diagnostic clinicalimaging, where it is highly desirable to perform non-mydriatic imaging,and pushing the pivot forward of the pupil is not a suitable solution.

Various embodiments of the improved retinal surgical lens assembly inaccordance with embodiments of the present inventive concept as well asrelated optical performance of these lens assemblies will now bediscussed with respect to FIGS. 19A through 23B. Each of theseconfigurations is designed to project the image of the scanning galvopair, which defines the OCT scan pivot, deeper into the eye below thepupil plane.

Referring first to FIG. 19A, a diagram of a surgical retina lensassembly having a 100 degree FOV in accordance with some embodiments ofthe present inventive concept will be discussed. As illustrated in FIG.19A, a microscope objective lens is coupled to a reduction lens with a20 mm spacing therebetween. The reduction lens is separated from the newretina lens 342 (FIG. 3) by a Spacing A (117 mm) and from the sample(eye) by a Spacing B (2.8 mm). Details of the lens designs and spacingsare found in the table on FIG. 19A. The retinal lens 342 typically has athickness of 6.6 mm from about 4 mm to about 10 mm, The system isdescribed operating at an IBZ NA setting of 69% of the high NA setting.

Referring now to FIG. 19B, a series of graphs and diagrams illustratingoptical performance of the surgical retina lens having a 100 degree FOVof FIG. 19A in accordance with some embodiments of the present inventiveconcept will be discussed. The OCT spot pattern as a function ofhalf-field of view is shown with the retina lens perfectly centered, andslightly decentered. The OCT beam has a center field beam diameter of 14um, increasing to 80 um at the edge of the field of view (+−8.5 um, or+−50 degrees). The maximum OPLD across the field of view is 1.9 mm,assuring a reasonably flat OCT image across this wide field. The visibleresponse for the microscope is also indicated at center field. Thelateral resolution of the visible signal is approximately 22 um.

Referring now to FIG. 20A, a diagram of a surgical retina lens assemblyhaving a 100 degree FOV in accordance with some embodiments of thepresent inventive concept will be discussed. As illustrated in FIG. 20A,an objective lens is coupled to a reduction lens with a 20 mm spacingtherebetween. The reduction lens is separated from a condenser 340 (FIG.3) lens by a Spacing A. The retina lens 342 (FIG. 3) is separated fromthe condenser lens 340 by a Spacing B and from the sample (eye) by aSpacing C. Details of the spacings are found in the table on FIG. 20A.

Referring now to FIG. 20B, a series of graphs and diagrams illustratingoptical performance of the surgical retina lens having a 100 degree FOVof FIG. 20A in accordance with some embodiments of the present inventiveconcept will be discussed. The OCT spot pattern as a function ofhalf-field of view is shown with the retina lens perfectly centered, andslightly decentered. The OCT beam has a center field beam diameter of 14um, increasing to 28 um at the edge of the field of view (+−8.5 um, or+−50 degrees). The maximum OPLD across the field of view is 1.9 mm,assuring a reasonably flat OCT image across this wide field. The visibleresponse for the microscope is also indicated at center field. Thelateral resolution of the visible signal is approximately 40 um. The OCTperformance is superior to the design of FIG. 19A, at a slight cost tothe visible resolution and to lens complexity.

Referring now to FIG. 21A, a diagram of a surgical retina lens assemblyhaving a 60 degree FOV in accordance with some embodiments of thepresent inventive concept will be discussed. As illustrated in FIG. 21A,an objective lens is coupled to a reduction lens with a 20 mm spacingtherebetween. The reduction lens is separated from the retina lens 342(FIG. 3) by a Spacing A and from the sample (eye) by a Spacing B.Details of the spacings are found in the table on FIG. 21A. The systemis described operating in the high NA setting.

In this embodiment, the surgical aspheric lens 342 is a singledouble-sided aspheric lens, sandwiching an additional thickness whichallows both surfaces to act as two individual lenses and providesadditional correction due to substantially different chief ray heightson both surfaces while reducing back reflections and optical complexityby having fewer surfaces that could potentially reflect more light. Itwill be understood that the aspheric lens cannot be made arbitrarilythick for a number of reasons. First, since this lens serves tocollimate outgoing light from the OCT system into the eye, it must notget too close to the retinal conjugate plane to avoid back reflectionsinto the OCT system. Second, if the lens were made so thick that theretinal conjugate plane was internal to the lens then the lens would beextremely difficult to fabricate. In addition, this lens has both of itssurfaces substantially symmetric in both base curvatures andeccentricities for somewhat reduced cost of fabrication.

In some embodiments, the P1 principle plane is 6.898 mm internal to thelens from the S1 surface while the P2 principle plane is −6.898 mminternal to the lens from the S2 surface and the lens is 21 mm thick.The relatively large distance of the principle planes from each surfaceis what allows substantially different chief ray heights at eachsurface. The maximum chief ray for OCT light is nearly telecentric nearthe retinal conjugate plane and makes an angle of 1.06 degrees with theoptical axis. The maximum chief ray height at S1 of the retinal surgicallens is 6.122 mm while the same chief ray at S2 is only 3.878 mm, whichallows each surface to nearly act as an individual lens. In someembodiments, the Base radii=25.697 mm (both convex); K=−3.679 (conicconstant); Thickness=21 mm; and EFL=18 mm at 587.6 nm.

Referring now to FIG. 21B, a series of graphs and diagrams illustratingoptical performance of the surgical retina lens having a sixty degreeFOV of FIG. 21A in accordance with some embodiments of the presentinventive concept will be discussed. The OCT spot pattern as a functionof half-field of view is shown with the retina lens perfectly centered,and slightly decentered. The OCT beam has a center field beam diameterof 8 um, increasing to 17 um at the edge of the field of view (+−5.5 um,or +−30 degrees). The maximum OPLD across the field of view is 0.9 mm,assuring a reasonably flat OCT image across this wide field. The visibleresponse for the microscope is also indicated at center field. Thelateral resolution of the visible signal is approximately 32 um.

Referring now to FIG. 22A, a diagram of a surgical retina lens assemblyhaving a 60 degree FOV in accordance with some embodiments of thepresent inventive concept will be discussed. As illustrated in FIG. 22A,an objective lens is coupled to a reduction lens with a 20 mm spacingtherebetween. The reduction lens is separated from the retina lens 342(FIG. 3) by a Spacing A and from the sample (eye) by a Spacing B.Details of the spacings are found in the table on FIG. 22A.

Referring now to FIG. 22B, a series of graphs and diagrams illustratingoptical performance of the surgical retina lens having a sixty degreeFOV of FIG. 22A in accordance with some embodiments of the presentinventive concept will be discussed. The OCT spot pattern as a functionof half-field of view is shown with the retina lens perfectly centered,and slightly decentered. The OCT beam has a center field beam diameterof 7 um, increasing to 9 um at the edge of the field of view (+−5.5 um,or +−30 degrees). The maximum OPLD across the field of view is 0.7 mm,assuring a reasonably flat OCT image across this wide field. The visibleresponse for the microscope is also indicated at center field. Thelateral resolution of the visible signal is approximately 45 um.

Referring now to FIG. 23A, a diagram of a surgical retina lens assemblyhaving a 80 degree FOV in accordance with some embodiments of thepresent inventive concept will be discussed. As illustrated in FIG. 23A,an objective lens is coupled to a reduction lens with a 20 mm spacingtherebetween. The reduction lens is separated from the retina lens 342(FIG. 3) by a Spacing A and from the sample (eye) by a Spacing B.Details of the spacings are found in the table on FIG. 23A.

Referring now to FIG. 23B, a series of graphs and diagrams illustratingoptical performance of the surgical retina lens having an 80 degree FOVof FIG. 23A in accordance with some embodiments of the present inventiveconcept will be discussed. The OCT spot pattern as a function ofhalf-field of view is shown with the retina lens perfectly centered, andslightly decentered. The OCT beam has a center field beam diameter of 12um, increasing to 16 um at the edge of the field of view (+−7.3 um, or+−40 degrees). The maximum OPLD across the field of view is 1.3 mm,assuring a reasonably flat OCT image across this wide field. The visibleresponse for the microscope is also indicated at center field. Thelateral resolution of the visible signal is approximately 48 um.

The embodiments of the present invention described above are general forthe integration of an OCT coupling element into the infinity space ofthe stereo zoom surgical microscope, folding into the imaging path ofthe microscope with a dichroic filter. The constraints have been limitedto access to this infinity space. An alternate embodiment is to directat least a portion of the optical path in parallel with the ocular pathsof the microscope, to minimize or eliminate the need to couple elementsinto the infinity space, thereby potentially obviating any impact to thesurgical working distances, and potentially yielding a more compact,streamlined multimodal imaging system. This implementation concept willbe referred to as a center-channel OCT (surgical) microscope (CCOM).

When considering how to construct a CCOM, i.e. to integrate an OCTsystem into a surgical stereo-microscope, the parameters that define theOCT beam should be defined. There are three primary parameters thatcharacterize the OCT beam: (1) the focused beam numerical aperture orNA; (2) the field of view over which the focused beam can be scanned;and (3) the degree of telecentricity of the focused beam over thescanned field. The equations governing how these parameters are relatedto microscope system parameters are discussed below with reference toFIGS. 24 through 27 below.

Referring first to FIG. 24, a diagram illustrating OCT telecentricityconditions in accordance with some embodiments of the present inventiveconcept. If telecentric scanning is required, then the telecentricconditions also need to be met: 1) the exit pupil of the OCT system liesin a focal plane of the microscope objective lens; and 2) the opticalaxes of the OCT and microscope objective lens are collinear.

NA_(O) is the OCT numerical aperture as defined by the focus beamhalf-angle; the maximum NA at which the OCT operates determines itslimiting lateral resolution. NA_(O) is represented by Equation (3) setout below:

${NA}_{O} = {\frac{1.22 \cdot \lambda_{O}}{2 \cdot \rho} = {\sin\;\beta}}$where β is the OCT focus beam half angle; λ_(O) is the OCT centerwavelength; and p is the OCT lateral resolution, assumed to be equal tothe Airy disk radius.ØB is the OCT collimated beam diameter, i.e. theOCT beam in infinity space between the exit pupil and the objectivelens. ØB is represented by Equation (4) set out below:

${{\varnothing\; B} \cong \frac{1.22 \cdot \lambda_{O} \cdot F}{\rho}} = {2\;{F \cdot {NA}_{O}}}$where F is the effective focal length of the surgical microscopeobjective lens and is tied to the scanned field of view ØV by Equation(5) set out below:

${{{F \cdot \tan}\;\alpha} = \frac{\varnothing\; V}{2}},$where tan α≈α for small angles, we have

${\alpha \cong \frac{\varnothing\; V}{2F}},$where α is me maximum scan angle of the OCT system. ØO is theField-of-view diameter of the OCT-microscope lens system.

ØA is the Clear aperture diameter on the objective lens required for theOCT beam and represented by Equation (6) set out below:ØA=ØB+ØV

Surgical stereo-microscopes typically use two or more afocal relay zoomlens (ARZL) systems looking through a common objective lens. Theindividual ARZL systems for left and right viewing channels have theiroptical axes parallel to and offset from the common objective lensoptical axis to provide stereopsis. Each viewing channel in the body ofa surgical stereo-microscope consists of the following key opticalsystems, listed in order starting from the object (or subject): 1) thecommon objective lens; 2) an afocal zoom relay system; 3) a tube lens toform an intermediate image; and 4) an erecting prism system to correctthe image orientation. The intermediate images for each viewing channelare imaged to final detectors—these can be either a surgeon's eyes orcameras—via binocular eyepiece lens systems. Since the binoculareyepiece systems are often designed to be exchangeable modules, theyneed not be considered when contemplating the integration of an OCTsystem into the surgical microscope. Furthermore, the erecting prismsystem and tube lens are usually standardized for a family ofstereo-microscope designs, which means that their parameters do notdrive the design of OCT system integration. This leaves the afocal relayzoom lens system and the objective lens as the optical systems ofprimary importance in driving integrated OCT system design.

Referring now to FIG. 25, a diagram illustrating Afocal Relay Zoom Lensconditions of a Surgical Stereo Microscope in accordance with someembodiments of the present inventive concept will be discussed. TheAfocal relay zoom lens system is characterized by 3 key parameters: (1)the operating NA at maximum magnification; (2) the field of view atminimum magnification; and (3) the zoom ratio, or ratio of maximum tominimum magnification. Since the afocal relay zoom lens system functionsin the infinity space above the objective lens, the magnification itprovides is purely angular. The equations listed below govern how theafocal relay zoom lens system parameters relate to the stereo-microscopesystem parameters.

NA_(m) is the microscope single viewing channel numerical aperture asdefined by the focus beam half-angle above; the maximum NA at which themicroscope operates determines its limiting lateral resolution. NA_(m)is represented by Equation (7) set out below:

${NA}_{m} = {\frac{1.22 \cdot \lambda_{m}}{2 \cdot r} = {\sin\;\delta}}$where δ is the Microscope viewing channel focus beam half angle; λ_(m)is the microscope viewing channel center wavelength; and r is theMicroscope viewing channel lateral resolution, assumed to be equal tothe Airy disk radius.

ØP is the Microscope viewing channel infinity space beam diameter and isrepresented by Equation (8) set out below:

${{\varnothing\; P} \cong \frac{1.22 \cdot \lambda_{m} \cdot F}{r}} = {2{F \cdot {NA}_{m}}}$where F is the effective focal length of the surgical microscopeobjective lens. M is the magnification of the afocal relay zoom lens andis represented by Equation (9) set out below:

$M = \frac{\tan\; ɛ}{\tan\;\gamma}$where γ is the object side chief ray angle for afocal relay zoom lensand c is the image side chief ray angle for afocal relay zoom lens.

γ₀ is the chief ray angle for object field point at edge of minimummagnification field of view and is represented by Equation (10) set outbelow:

${\gamma_{o} \cong {\tan\;\gamma_{o}}} = \frac{\varnothing\; Q}{2F}$where ØQ is the diameter of microscope field of view at minimummagnification.

z is the Afocal relay zoom lens magnification ratio (typically z=6 forsurgical stereo-microscopes) and is represented by Equation (11) set outbelow:

$z = {\frac{M_{m}}{M_{o}} = {{\frac{\tan\; ɛ_{m}}{\tan\; ɛ_{o}} \cdot \frac{\tan\;\gamma_{o}}{\tan\;\gamma_{m}}} = {\frac{\tan\; ɛ_{m}}{\tan\; ɛ_{o}} \cdot \frac{\varnothing\; Q}{\varnothing\; R}}}}$where M_(m) is the maximum afocal relay zoom lens magnification; M_(o)is the minimum afocal relay zoom lens magnification; γ_(m) is the chiefray angle for object field point at edge of maximum magnification fieldof view; ε_(m) is the Chief ray angle on image side of afocal relay zoomlens for γ_(m) input (max. magnification); ε_(o) is the Chief ray angleon image side of afocal relay zoom lens for γ_(o) input (min.magnification); and ØR is the diameter of microscope field of view atmaximum magnification.

Equation (12) set out below illustrates how the full-field chief rayangles on the object side of the afocal relay zoom lens are related atthe zoom extremes.

${\gamma_{m} \cong {\tan\;\gamma_{m}}} = {\frac{\tan\;\gamma_{o}}{z} \cong \frac{\varnothing\; Q}{2{zF}}}$

For a well-designed afocal relay zoom lens, the apparent location of theimage should not change as the magnification is varied. This conditionis expressed by Equation (13) set out below:

$\frac{\tan\; ɛ_{m}}{\tan\; ɛ_{o}} = {1\mspace{14mu}\left( {{well}\mspace{14mu}{designed}\mspace{14mu}{zoom}} \right)}$

With the performance conditions of a stereo zoom surgical microscopedefined, constraints and design conditions for a CCOM can be defined.

Referring now to FIG. 26, a diagram illustrating conditions of a centerchannel OCT-integrated Surgical Stereo Microscope (CCOM) in accordancewith some embodiments of the present inventive concept will bediscussed. One way to integrate an OCT system into a surgicalstereo-microscope while satisfying the telecentric scanning conditionsdescribed above is to make room for the OCT beam centered on theobjective lens optical axis with the ARZL systems (2 or 4, depending onwhether there are dedicated viewing channels for an assistant to thesurgeon) offset from the objective lens optical axis by a minimumdistance that allows the OCT beam path to stay clear. In someembodiments, the barrel of the ARZL system just touches the OCT beam atmaximum scan angle. In these embodiments, the minimum ARZL offset andminimum objective lens edge diameter can be calculated according to theequations discussed below.

This first-order analysis assumes that the exit pupil of the ARZL iscoincident with the bottom lens and mechanical barrel. In reality thiswill not be the case, but this is a close approximation.

ØE is the minimum edge diameter of microscope objective lens that willfit an OCT system and ARZL system with given parameters and isrepresented by Equation (14) set out below:

$\frac{\varnothing\; E}{2} = {d_{1} + d_{2} + d_{3} + d_{4}}$where d₁ . . . d₄ are lateral distances as shown in FIG. 26 with exactrelations given individually below.

O is the offset of ARZL optical axis from objective lens optical axisand is represented by Equation (15) set out below:

$O = {d_{1} + d_{2} + \frac{\varnothing\; G}{2}}$where ØG is the ARZL mechanical barrel diameter.

The distance d₁ from objective lens optical axis to OCT beam chief rayat maximum scan angle measured in the plane of the exit pupil of theARZL is represented by Equation (16) set out below:d ₁=(F−H)·tan αwhere H is the height of the ARZL above the objective lens.

The distance d₂ from the OCT beam chief ray at maximum scan angle to theedge of the ARZL mechanical barrel measured in the plane of the exitpupil of the ARZL when the OCT beam just grazes the ARZL barrel isrepresented by Equation (17) set out below:

$d_{2} = \frac{\varnothing\; B}{2\;\cos\;\alpha}$

The distance d₃ from the inside edge of the ARZL barrel to the outsideedge of the full-field viewing channel ray bundle measured in the planeof the ARZL exit pupil is represented by Equation (18) set out below:

$d_{3} = \frac{{\varnothing\; G} + {\varnothing\; P}}{2}$

The distance d₄ from the outside edge of the full-field viewing channelray bundle to the edge of the objective lens measured in the plane ofthe ARZL exit pupil is represented by Equation (19) set out below:d₄=H tan γ_(m)

The full expression for the minimum objective lens diameter needed tofit a centered OCT channel surrounded by ARZL(s) with the givenparameters is represented by Equation (20) set out below:

${\varnothing\; E} = {{\varnothing\;{V\left( {1 - \frac{H}{F}} \right)}} + {2{NA}_{OCT}\sqrt{F^{2} + \left( \frac{\varnothing\; V}{2} \right)^{2}}} + {F \cdot {NA}_{AZ}} + {\varnothing\; G} + {H \cdot \frac{\varnothing\; Q}{z \cdot F}}}$

For the highest NA (high resolution) OCT systems, the ARZL offsets andobjective lens diameters may need to be impractically large. In suchcircumstance, it may be desirable to design a hybrid between theinfinity-space coupled design and the CCOM design for a folded-pathcenter-channel OCT (surgical) microscope (FCCOM).

Referring now to FIG. 27, a diagram illustrating conditions of foldedpath center channel OCT-integrated Surgical Stereo Microscope (FCCOM) inaccordance with some embodiments of the present inventive concept willbe discussed. In these embodiments, a dichroic mirror is used in thespace between the ARZL and the objective lens to fold in the OCT beam,while the microscope viewing paths look through it. A goal is tominimize the space required to accomplish this fold, primarily to reducethe height of the microscope body. The minimum height is achieved whenthe incidence angle, φ, is a minimum. For the extreme case where thedichroic mirror just touches the outside edge of the objective lens andthe folded OCT beam just touches the opposite edge of the objectivelens, the minimum angle condition is given by Equation (21) set outbelow:

$\frac{\left( {E + A} \right) \cdot {\cos\left( {{2\varphi} + \alpha} \right)}}{\sin\left\lbrack {2\left( {\varphi + \alpha} \right)} \right\rbrack} = \frac{{\left( {E - A} \right) \cdot \sin}\;\varphi}{\cos\left( {\varphi + \alpha} \right)}$

This equation is non-linear and cannot be solved analytically, but canbe solved numerically. For typical surgical stereo-microscope and highNA OCT parameters, φ_(min) works out to be approximately 37°. Note thatin this geometry, the angle φ is related to the dichroic angle asdescribed in Eqn. (1) above by φ=90°−θ, and therefore the maximum valueof θ is approximately 53°.

It is not necessary that the folding dichroic mirror extend across theentire diameter of the common objective lens. If the ARZL systems arelocalized, then the dichroic mirror need only be large enough to notclip the microscope viewing channels. This arrangement may haveadvantages for introducing illumination of the focal plane via thedichroic and/or fold mirrors. In conventional surgicalstereo-microscopes the illumination systems are typically introduced inthe space between ARZL and objective lens. Thus, in the folded OCTconfiguration this space can be used for a dual purpose: illuminationand coupling of the OCT system while minimizing impact to surgicalworking distances, in accordance with embodiments discussed herein.

Referring now to FIG. 28, a flowchart illustrating a method of imagingusing a surgical microscope in accordance with some embodiments of thepresent inventive concept will be discussed. Operations begin at block2800 by selecting a region of interest (ROI) in the sample, for example,an eye, with a ROI being one of a cornea, a lens, an anterior segment, aposterior segment, a retina, or the like. A microscope main objectiveand any accessory lenses are selected and configured to the microscopesystem (block 2810), for example, an optimized 175 mm focal lengthobjective and a 100 degree surgical retinal lens. If required, the OCTpath may be adjusted such that the back focal length matches theobjective lens (block 2820). The reference arm is adjusted accordingly(block 2830) such that the reference arm path length matches the OCTpath length to the ROI. The numerical aperture (block 2840) is adjustedso that image brightness meets the surgical uniformity requirement andlateral resolution meet the surgical resolution requirements. Focus(block 2850) is adjusted so that the optimum focus is targeted at thedepth of interest within the ROI; the focal position may be at themicroscope focal plane, or above or below this plane according to needsof the surgeon. The image, images, or continuous video display isobtained (block 2860) using these settings. A determination is madewhether the desired image(s) have been obtained (block 2870). If thedesired images have been obtained (block 2870) with the desired imagequality, operations may cease until another image is desired. If, on theother hand, it is determined that desired image(s) have not beenobtained, operations return to block 2840 and repeat until the desiredimages and image quality are obtained.

Referring now to FIG. 29, a flowchart illustrating a method of imagingduring a surgical procedure using an OCT-integrated surgical microscopein accordance with some embodiments of the present inventive concept. Asillustrated in FIG. 29, operations begin at block 2905 by selecting aROI to be imaged in the sample, for example, the eye, and as describedabove. The reference arm is adjusted (block 2915). The NA forresolution/brightness uniformity (block 2925) and the focus forbrightness (block 2927) are adjusted. Images are acquired using thecurrent settings (block 2935). An initial set of clinical parameters arecomputed based on the current settings and the acquired images (block2937).

These clinical parameters may include a shape of an anterior surface ofa cornea, the shape of an anterior stromal surface of a cornea, theshape of an endothelia surface of a cornea, and any relevant parametersthat may be derived from such measures, including but not limited topachymetry maps, curvature maps, refractive powers, aberration maps,keratometry values and the like. Clinical parameters may further includean iridocorneal angle, a sclera thickness, a bleb geometry, a Canal ofSchlemm position and the like. Clinical parameters may also include apupil diameter, a lens capsule thickness, a lens thickness, or the like.Clinical parameters may still yet include a retinal membrane area orthickness, a thickness of a particular retinal layer, the geometry of aparticular pathology in the retina, or the like. Clinical parameters maybe any such parameter directly observable and measurable with an OCTimaging system, or parameters derived from such direct observables.

The surgical protocol is designed using at least in part one or more ofthese clinical parameters for guidance. The surgical procedure isinitiated using the initial parameters (block 2945). The NA (block 2947)and the focus for brightness on procedure ROI (block 2955) are adjustedto optimize visualization of the procedure. Additional images areacquired (block 2957), and the surgical procedure continues at least inpart in response to the visualized OCT images. The NA (block 2965) andthe focus for brightness on procedure ROI (block 2967) are adjusted, ifneeded, either to improve the image quality, or to observe structuresthat may be secondarily impacted by the procedure. For example, during acataract procedure, it may be desirable to visualize the retina toobserve any traction transmitted to the retina. Secondary implicationsobservable to the surgeon with the OCT will be understood by the surgeonas expert in the art. More images are acquired using the new settings(block 2975). As the procedure nears completion, a new set of clinicalparameters are computed based on the subsequently acquired images andassociated settings (block 2977). The initial clinical parameters andthe new clinical parameters are compared (block 2985) and adetermination whether the desired results have been achieved is made(block 2987). If the desired results have been achieved (block 2987),operations cease. If, on the other hand, the desired results are notachieved (block 2987), then operations return to block 2945 and repeatuntil the desired results are achieved.

As an adjunct to controlling the OCT depth of field through NA control,the (Fourier domain) window depth may adjusted by controlling thespectral sampling interval, as illustrated in FIG. 30. Referring now toFIG. 30, a series of charts illustrating image depth of field adjustmentthrough selection of spectral sampling interval in accordance with someembodiments of the present inventive concept will be discussed.

As is now well known in the art, the FDOCT image window is a function ofthe spectral sampling interval. The maximum observable image windowdepth corresponds to the minimum spectral sampling interval. In aspectral domain system, a spectrometer pixel spacing constrains theimage depth. In a swept source system, hardware constraints on spectralsampling set the constraint. On the other hand, the observable imagedepth may be halved or quartered by doubling or quadrupling the spectralsampling interval. With a fixed spectral range, the resolution is notimpacted, the window depth is reduced, and the number of pixels iscorrespondingly reduced. This process has the advantage of displayingonly the region of interest, when a constrained region of interest istargeted, and may do so at less computation cost, because the number ofdata points is reduced. In this fashion, there is increased focus on theregion of interest, reduced computational cost, and potentially fasteracquisition and display for faster feedback to the surgeon.

Referring now to FIG. 31, a diagram illustrating one embodiment of anOCT optical system in accordance with some embodiments of the presentinventive concept will be discussed. In this embodiment, the system wasconfigured to correct for higher-order aberrations over the requiredscan range, resulting in the system shown in FIG. 31. This opticalsystem design was fine-tuned to reduce back-reflections that coupleefficiently into the source fiber in order to reduce noise in the OCTsignal. The system illustrated in FIG. 31 contains 13 singlets and 7doublets (all with spherical surfaces) which can be folded up to fitinto a 50 mm×125 mm×150 mm volume.

Finally, OCT optical systems in accordance with some embodimentsdiscussed herein can perform optimally for the specific microscopeobjective or range of microscope objectives for which it is designed. Incontrast to both diagnostic ophthalmic OCT systems and laboratorymicroscopes, surgical microscopes have very long working distances,ranging typically from about 150 mm to about 175 mm, but extending fromabout 125 mm to about 200 mm. Furthermore, the concept of OCTintegration into laboratory microscopes has already been commercializedby Bioptigen, as illustrated in FIG. 1D for a system with a 75 mmobjective focal length. Additionally, the microscope objective isdesigned with demands of surgical imaging (or laboratory imaging) andcolor correction in mind. These design objectives are not alwaysimmediately consistent with the requirements of high quality OCTimaging. Further, the variety of surgical systems and applications meansthat this OCT interface must adapt to a wide variety of microscopeobjectives, laboratory, and surgical applications.

To provide the most flexible OCT interface, the architecture of thesystem is divided into two subsystems that we will call the OCT Relayand the OCT Objective. The OCT Relay as described provides flexibilityin controlling the numerical aperture and focal control of the OCTsystem. The OCT Objective is the final multiple-lens system thatincludes the microscope objective and sets the exit pupil of the OCTsystem, including any back focal length accommodation. The exit pupilshould be positioned at the front focal plane of the microscopeobjective. The OCT Objective can be tailored to any microscopeobjective, with the virtual exit pupil reducing the mechanicalconstraints of placing a real exit pupil. Additionally the multi-lenselement preceding the microscope objective is useful for setting a focalbias to the OCT system relative to the microscope system, allowing thefocal control of the Input Beam Zoom to optimize the focus around thisbias point for increased control and optimization of the OCT image.

The features of the present inventive concept extend the range ofutility of this Microscope OCT interface from the long working distanceof a surgical microscope to the shorter working distances of alaboratory microscope.

Example embodiments are described above with reference to block diagramsand/or flowchart illustrations of systems and devices. Thefunctions/acts noted in the blocks may occur out of the order noted inthe flowcharts. For example, two blocks shown in succession may in factbe executed substantially concurrently or the blocks may sometimes beexecuted in the reverse order, depending upon the functionality/actsinvolved. Moreover, the functionality of a given block of the flowchartsand/or block diagrams may be separated into multiple blocks and/or thefunctionality of two or more blocks of the flowcharts and/or blockdiagrams may be at least partially integrated.

In the drawings and specification, there have been disclosed exemplaryembodiments of the inventive concept. However, many variations andmodifications can be made to these embodiments without substantiallydeparting from the principles of the present inventive concept.Accordingly, although specific terms are used, they are used in ageneric and descriptive sense only and not for purposes of limitation,the scope of the inventive concept being defined by the followingclaims.

That which is claimed is:
 1. An optical coherence tomography (OCT)system for integration with a microscope, the microscope includingviewing oculars, a body and an imaging objective lens, the OCT systemcomprising: a source of broadband optical radiation, a beamsplitterdividing the source radiation into a reference path and a sample path, abeamsplitter that mixes source radiation reflected from a subject in thesample path with source radiation returned from a reference reflector inthe reference path to create a wavelength dependent interferogram thatis directed along a detection path to a detection module, wherein thesample path includes a sample arm coupled to a viewing path of amicroscope, the sample arm comprising: an optical fiber that delivers anOCT beam of optical radiation transmitted from the source of broadbandoptical radiation along the sample path to a scanning optical system andreceives light from the scanning optical system that has beenbackscattered from a sample, wherein the scanning optical systemincludes an input beam zoom assembly including at least two movablelenses configured to provide shape control for an OCT beam of opticalradiation, wherein the input beam zoom is positioned along the pathbetween the optical fiber and a first mirror of a dual-axis scanassembly; wherein the dual-axis scan assembly scans the OCT beam ofoptical radiation along two orthogonal directions perpendicular to theoptical axis of the OCT system; and an afocal beam expander positionedalong the path between the scan assembly and the microscope objectivelens, wherein the microscope objective lens is positioned in the opticalpath shared in common by the OCT system and the microscope; wherein theoptical system in the OCT sample arm path following the optical fiberand including the input beam zoom, the optical scan assembly, the afocalbeam expander and the microscope objective lens provide forsubstantially telecentric scanning of the OCT beam of optical radiationabout two axes orthogonal to the optical axis of the microscopeobjective lens; wherein the OCT system comprises a controller forchanging the positions of the movable lenses of the input beam zoomassembly to independently set a numerical aperture and focal position ofthe imaged OCT beam; wherein the sample is an eye; wherein a retinalimaging lens assembly is situated between the microscope objective lensand the eye; and wherein the retinal imaging lens assembly images aconjugate of the scanning mirrors to a position posterior to a pupilplane of eye.
 2. The OCT system of claim 1, wherein the OCT signal beamis coupled to the microscope imaging path through a dichroicbeamsplitter.
 3. The OCT system of claim 2, wherein the beamsplitter isset at an angle of not less than 48 degrees and not greater than 55degrees relative to the optical axis of the microscope objective lens.4. The OCT system of claim 1, wherein the afocal beam expander comprisesan aberration compensator.
 5. The OCT system of claim 1, wherein a pathlength adjustment is included in the sample arm between the afocal beamexpander and the microscope objective lens to accommodate for variationsin the focal length of the microscope objective lens.
 6. The OCT systemof claim 1, wherein the telecentric scan assembly comprises a firstscanning mirror having an image relayed onto a second scanning mirrorand wherein an exit pupil of the OCT sample arm is in the back focalplane of the microscope objective lens.
 7. The OCT system of claim 6,wherein the exit pupil of the OCT sample arm optics comprise a virtualexit pupil.
 8. The OCT system of claim 1: wherein the input beam zoomcomprises first and second positive lenses and a negative lenstherebetween; and wherein a numerical aperture of the system is set bycontrolling a first distance between the first positive lens and thenegative lens and a second distance between the negative lens and thesecond positive lens.
 9. The OCT system of claim 8, wherein a focus ofthe OCT system is set by controlling a position of the second positivelens for a particular setting of numerical aperture.
 10. The OCT systemof claim 1: wherein at least a portion of the OCT sample path occupies acenter channel of the body of the microscope; wherein the OCT beam ofoptical radiation is directed towards a center field of the microscopeobjective lens; and wherein any ocular paths of the microscope aresituated peripherally to this center field of the microscope objectivelens.
 11. The OCT system of claim 2, wherein the beamsplitter occupiesan area less than a clear aperture of the microscope objective lens. 12.The OCT system of Claim 1, wherein retinal imaging lens assemblyincludes at least one lens with at least one aspheric surface.
 13. TheOCT system of claim 1, further comprising an objective lens in commonwith a microscope, wherein the objective lens is anti-reflection coatedfor operation in a visible spectral range relevant to the microscopevisualization and an infrared spectral range relevant to the OCT system.14. The OCT system of claim 13, wherein the microscope objective lens isan achromatic doublet comprising a crown glass positive lens componentand flint glass negative lens component.